1. Field of the Invention
The present invention generally relates to a method and apparatus of fabricating electromagnetic coil vanes and, more particularly, to a method and apparatus for fabricating high precision, thermally stable electromagnetic coil vanes used with Charged Particle Beam Projection Systems.
2. Background Description
Yokes and electromagnetic lenses are widely used in electron beam tools, electron microscopes, and cathode ray tubes. Yokes and lenses employing toroidal magnetic deflection coils are commonly used in electron beam lithography systems for focusing an electron beam on to a substrate for submicron patterning of semiconductor devices.
U.S. Pat. No. 4,251,728 to Pfeiffer shows an example of a toroidal magnetic deflection yoke. FIG. 1 shows a top view of a traditional toroidal yoke similar to that shown in Pfeiffer. The traditional yoke includes a plastic form having slots numbered from 1 to 20, and forms both X and Y coil axes.
Presently, electromagnetic coils are formed by winding wire into multiple radial grooves cut from a plastic form. Also, deflection yokes have been made from round wire, with bondable insulative coatings. The method used for winding the form to make the coils requires alternating between the X and the Y windings. As the number of radially cut grooves and the number of turns increases, so does the degree of difficulty and the time involved. Accordingly, current methods used for winding coils is difficult and time consuming, particularly when the number of offset grooves and turns increases.
It is therefore an object of the invention to provide a method and apparatus for fabricating high precision, thermally stable electromagnetic coil vanes.
According to the invention, a method and apparatus are provided to fabricate high current capacity, high accuracy, thermally stable deflection yokes used to generate off axis beam deflections.
In the preferred embodiment, electromagnetic coil vanes are fabricated having two complementary patterns of approximately 22-23 American Wire Gauge (AWG), uninsulated rectangular cross section wire to be accurately bonded to a thin substrate. Preferably, the coefficient of thermal expansion (CTE) of the thin substrate should be low. For example, quartz can be used, which has a CTE of approximately 0.56xc3x9710xe2x88x926/xc2x0 C. The two complementary copper coil patterns are connected by a through wire. The through wire provides an electrical connection between the two copper coil patterns. The gaps between adjacent copper wires must be as small as possible to maximize the copper density and thus the coil""s effectiveness.
The method involves placing a bonding composition on opposing surfaces of a substrate. First and second complementary copper coil patterns are formed, aligned and bonded to respective clamp plate fixtures. The first complementary copper coil pattern is bonded to one surface of the opposing surfaces of the substrate via the bonding composition, and the second complementary copper coil pattern is bonded to the other surface of the opposing surfaces of the substrate via the bonding composition. The bonding composition is cured, and the clamp plates are removed from the first and second complementary copper coil patterns.